Wide tread radial tire-rim assembly with bead-rim interlock

ABSTRACT

The present invention relates to a radial tire and a radial tire-rim assembly. The radial tire (1) has a pair of beads (2), each bead having a bead core (3) and a bead apex (5), a carcass (4), with both edges thereof folded back around said bead core and fastened to said bead core, a tread (6), a belt layer (7), and an aspect ratio smaller than 60%. The tread is wider (in the axial direction) than the maximum width of said carcass and the edges of said tread are positioned within a range of 50-100% of the height of the cross-section of the carcass. This structure provides the tire side with rigidity and permits the tread to deform so that it supports the weight of the car and runs safely even when the tire pressure is decreased. The radial tire-rim assembly is characterized in that the bead of the radial tire has a toe (9) extending inward (in the radial direction of the tire) and is further provided with a hump groove (10). Correspondingly, the rim (20) has an annular groove (22) and hump (23) which fit into the toe and groove, respectively. These arrangements prevent the bead from separating from the rim when the tire pressure is decreased or at a time of sharp cornering.

This application is a continuation of application Ser. No. 07/144,924filed as PCT/JP00278 on May 11, 1987, published as WO87/06891 on Nov.19, 1987, now abandoned.

TECHNICAL FIELD

The present invention relates to a radial tire, and more particularly,it relates to a so-called safety tire for four-wheeled cars whichpermits the driver to continue safe driving even when the tire pressurehas suddenly decreased due to puncture with a nail or otherwise burstsbecause it supports the weight of the car with the rigid side and thedeformable tread. The present invention also relates to a radialtire-rim assembly which keeps the beads in place on the rim even in thecase of puncture or at the time of sharp cornering.

BACKGROUND ART

There have been proposed several kinds of tires designed to be safe evenin the case of a puncture or other loss of air pressure. They include,for example, a safety tire having a support of elastic material in thetire, a dual structured tire having an independent toroidal air-tightcompartment in the tire, and a reinforced tire with the side wall orshoulder reinforced with an elastic reinforcing layer attached to theinside thereof.

The first two types have a problem with increased weight (undesirablefor a high-speed tire) and increased production cost. The last type isnot strong enough to firmly support the load.

Accordingly, it is an object of the present invention to provide a newradial tire which, despite its structure is entirely different from thatof the above-mentioned conventional tires, provides as good a ridecomfort and stable maneuverability as the ordinary tires during normaldriving conditions and yet continues to run safely even when the tirepressure abruptly decreases due to puncture during high speed driving ona highway.

For safe driving, the tire should be firmly held in position on the rim.Heretofore, this has been achieved mainly by the frictional force whichis generated between the bead and the bead seat as the bead is pressedagainst the bead seat by the tire pressure. Therefore, the power to holdthe tire on the rim decreases as the tire pressure decreases. In anextreme case where the tire pressure has decreased rapidly due topuncture and the steering wheel is quickly turned, the tire beadseparates from the bead seat and falls into the well on account of thelateral force applied to the tire. As a result, the tire is completelydisplaced, which leads to a serious accident.

The separation of the tire bead takes place in the following sequence.The cornering of the car produces a lateral force which moves the treadin the axial direction of the rim. The movement of the tread produces amoment of rotation around the bead. When the tire pressure is low, themoment of rotation lifts the heal of the bead, and decreases thefrictional force between the bead and the bead seat to such an extentthat the bead slips out of place in the inward direction of the tireaxis. In this state, the bead core loses tension for keeping the tire onthe rim and thus falls into the well.

It is another object of the present invention to provide a radialtire-rim assembly which can run safely even when the tire pressure hasdecreased. The feature of the radial tire-rim assembly is due to theunique structure of the tire and rim. That is, the bead has a toeextending inward in the radial direction of the tire and the rim has anannular groove to mate with said toe. The toe-groove combinationprevents the bead from falling into the well when the bead receives alateral force.

DISCLOSURE OF THE INVENTION

The present invention provides a radial tire having a pair of beads,each bead having a bead core, a carcass extending across said beads,with both edges thereof folded back around said bead core and fastenedto said bead core, one each of bead apex arranged between the foldedpart and the carcass proper, a tread arranged outside (in the radialdirection of the tire) of said carcass, a belt layer arranged betweensaid carcass and said tread, said belt layer having cords arrangedslightly aslant with respect to the circumferential direction of thetire, and an aspect ratio (the height of the tire cross-section dividedby the maximum width of the tire) smaller than 60%, said radial tirebeing characterized in that said tread is wider (in the axial direction)than the maximum width of said carcass and the edges of said tread arepositioned within a range of 50-100% of the height of the cross-sectionof the carcass ply.

The present invention also provides a radial tire-rim assembly made upof said radial tire and a rim having a well to facilitate the mountingof the tire, said radial tire being characterized in that at leasteither of the beads is provided in a portion axially inward of the beadcore with a toe which extends radially inwardly therefrom, and providedon the axially outside of the toe with a hump groove, and said rim beingcharacterized in that it has an annular groove to receive the tip of thetoe and a hump to fit into said hump groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the right half of an example of theradial tire of the present invention.

FIG. 2 is a perspective view of the radial tire of the invention.

FIG. 3 is a schematic sectional view of the radial tire-rim assembly ofthe invention, with the tire pressure decreased.

FIG. 4 is a fragmentary sectional view of the radial tire-rim assembly.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be described with reference to an example shownin the drawings.

In the drawings, there are shown the radial tire 1, paired beads 2 eachhaving the bead core 3, the carcass 4 extending from one bead 2 to theother, the tread arranged outside (in the radial direction of the tire)the carcass 4, and belt layer 7 arranged between the carcass 4 and thetread 6.

The radial tire of the present invention has an aspect ratio smallerthan 60%, which is defined by dividing the height of the cross-sectionof the tire by the maximum width of the tire.

The carcass 4 has at least one layer of carcass ply composed of radiallyarranged cords. Each edge of the carcass is folded back (from inside tooutside in the axial direction of the tire) around the bead core 3 andfastened to the bead core 3.

The first feature of the radial tire of the present invention resides inthat the tread 6 extends to that part of the tire which corresponds tothe side wall of the conventional tire. In other words, the tread 6 hassuch dimensions that the width TW (in the axial direction) is greaterthan the maximum width L of the carcass 4, and the height ho of thetread end P is within the range of 50 to 100% of the height h of thecross-section of the carcass 4.

In addition, the thickness of the tread 6 at both edges is within therange of 70 to 200% of the average value of the thickness CW at thetread center and the thickness NW at the position three quarters of themaximum width L of the carcass 4 measured from the tread center. If itis smaller than 70%, the tire does not have sufficient rigidity toensure safe running when the tire pressure has decreased; and if it ishigher than 200%, the tire generates excessive heat during high-speedrunning.

The structure as mentioned above provides the difference in rigiditywhich functions as a hinge to join the tread and the tire side. Thus,when the tire pressure decreases, the tread and the tire side turn onthe hinge as shown in FIG. 3, and the tread 6 as a whole becomes flat toensure safe running.

The extended part 6A of the tread 6 is formed in a rug pattern or ablock pattern and is provided with sipings or fine grooves S to increaseheat dissipation as shown in FIG. 2. The sipings or fine grooves S areformed in the region corresponding to 5 to 20% of the curved distance TLfrom one tread end P to the other tread end along the surface of thetread 6. Their interval is 5 to 20 mm and their width is 0.1 to 5 mm. Ifthey are formed at an angle of 45 to 90 degrees with respect to thecircumferential direction of the tire, they promote heat dissipation,and if their angle is 0 to 45 degrees, not only do they promote heatdissipation but they lower the vertical spring constant which leads toimproved ride comfort. Thus the angle is selected according to theapplication.

The belt layer 7 is arranged between the carcass 4 and the tread 6, andit has cords arranged slightly aslant with respect to thecircumferential direction of the tire. In this example, the cords arecomposed of low-modulus organic fiber cords (forming the plies 7A and7B) and high-modulus organic or inorganic fiber cords (forming the ply7C).

The width of the belt layer 7 (or the width of the plies 7A and 7B inthis example) is within the range of 70 to 100% of the curved distanceTL along the surface of the tread 6. The belt layer 7 extended to bothedges of the tread 6 reinforces the tread 6 even when the tire pressurehas decreased and the tread 6 has become flat, so that the flat tirecontinues to run for a long time.

The low-modulus organic fiber cords include those of nylon, polyester,and rayon which have an elastic modulus lower than 1000 kg/mm². Theorganic fiber cords of low elastic modulus are preferably used becausethe same ply produces the "hoop effect" on the crown, shoulder, and sidewhich differ from one another in the radius of curvature.

The high-modulus fiber cords include aramid cords and steel cords. Theply 7C composed of the high-modulus fiber cord should have a width whichis smaller than 80% of the maximum width L of the carcass 4.

The bead 2 is composed of the non-extensible bead core 3, the bead apex5, the toe 9 which extends inward (in the radial direction of the tire),and the hump groove 10.

The bead core 3 is positioned outside (in the axial direction of thetire) unlike that of the conventional radial tire. This is one of thefeatures of the present invention. The bead core 3 is positioned suchthat the distance w4 from the center of the bead core 3 to the heal endJ is 1/2.5 to 1/7.6, preferably 1/2.9 to 1/6.3 of the distance betweenthe heal end J and the toe end N. In the case of conventional tires, itis about 1/2.2 at the shortest. Incidentally, the heal end J is thepoint at which the prolonged line of the outer surface Q of the bead 2intersects the prolonged line of the bottom surface M. The advantage toreducing the distance W4 is that the bead core 3 is close to the rimflange 25 and the bead firmly fits into the rim 20.

The bead apex 5 is made of rubber having a hardness of 74° to 95°,JIS(A). It is arranged between the carcass proper 4B and the folded part4A of the carcass, and it extends outward (in the radial direction ofthe tire) from the bead core 3. The bead apex 5 is as high as 70-90%,preferably 40-110%, of the height ho up to the end P of the tread 6. Abead apex longer than 110% is not preferable because it hinders theabove-mentioned hinge action. The bead apex of the specified lengthmaintains the rigidity of the tire side when the tire pressure hasdecreased, thereby permitting the safe driving.

The toe 9 projects inward (in the radial direction of the tire) from thebottom surface 7 of the bead 2 at the portion being inward (in the axialdirection of the tire) of the bead core 3.

The amount L of projection is properly selected according to the use andsize of the tire. The toe 9 is made of comparatively hard rubber havinga hardness of 70°-85°, JIS(A).

The hump groove 10 is formed outside (in the axial direction of thetire) the toe 9, and it extends in the circumferential direction of thetire. The distance W5 (in the axial direction of the tire) between thehump groove 10 and the heal end J is 2.1 to 4.8 times the distance W4(in the axial direction of the tire) between the heal end J and thecenter of the bead core 3. The hump groove 10 permits the radial tire 1of the present invention to snugly fit into the rim 20 having the hump23 (mentioned later). The radial tire of the invention can also fit intoa rim without the hump 23.

The rim 20 has the well 21 at the center and the annular groove 22, hump23, bead seat 24, and rim flange 25 formed in the order mentionedoutside the well. The annular groove 22 is adjacent to the well 21, andit extends in the circumferential direction of the tire. Therefore, theprotuberence 26 extending in the circumferential direction is formedinside the annular groove 22. The height h1 of the protuberence 26should preferably be 5 mm or less from the bead seat 24. The top of theprotuberence 26 may be below the bead seat 24.

The bottom of the annular groove 22 should be inward (in the radialdirection of the tire) from the bead seat 24, and the depth d shouldpreferably be 10 mm or less from the bead seat 24. In addition, theannular groove 22 should be positioned such that the relationshipW6/W3=0.7 to 1.2 is established, where W6 is the distance between theheal end J and the toe end N and W3 is the distance between the deepestpart of the annular groove 22 and the end H of the bead seat 24. The endH of the bead seat 24 is the point at which the prolonged line of thebead seat 24 intersects the prolonged line of the inner surface of therim flange 25.

The hump 23 is formed such that the relationship W5/W2=0.5 to 1.2 isestablished, where W5 is the distance (in the axial direction of thetire) between the hump groove 10 and the heal end J and W2 is thedistance (in the axial direction of the tire) between the outermost end(in the radial direction of the tire) of the tire and the end H of thebead seat. The height h2 of the hump 23 should preferably be smallerthan 5 mm from the bead seat 24.

The bead seat 24 is slightly tapered inward (in the axial direction ofthe tire) at a certain angle (α) as shown in FIG. 4. The bead seat mayalso be inversely tapered, if necessary.

The width W1 of the bead seat 24 conforms to the existing standards, sothat the rim 20 fits into the radial tire of the invention as well asthe radial tire of conventional structure.

The toe 9 and hump groove 10 of the radial tire 1 and the annular groove22 and hump 23 of the rim 20 should have proper shapes and dimensions sothat they snugly fit into each other. In addition, the diameter of therim at different parts should be determined so that the followingrelationships are established.

    -3.0mm≦D-Da≦+5.0mm

    +2.0mm≦D-Db≦+2.0mm

    0.0mm≦D-Dc≦+5.0mm

    Da>Dc>Db

wherein D is the diameter at the end H of the bead seat, Da is thediameter at the hump 23, Db is the diameter at the bottom of the annulargroove 22, and Dc is the diameter at the protuberence 26, as shown inFIG. 4.

The diameter Da at the hump is made greater than the diameter Dc at theprotuberence so as to facilitate the fitting of the tire bead.

As mentioned above, the radial tire of the present invention has atread, with both edges extending to the tire sides. Therefore, the treadbecomes flat and comes into contact with the ground as schematicallyshown in FIG. 2 when the tire pressure has decreased due to puncture,thereby preventing the side from coming into contact with the ground andprotecting it from damage by the contacting with the ground. Inaddition, the side having increased rigidity supports the weight of thevehicle. Therefore, the radial tire of the invention permits safedriving even with the tire pressure decreased.

The radial tire-rim assembly of the invention, which is characterized bythat the radial tire has the toe extending inward (in the radialdirection of the tire) and the rim has the annular groove to mate withthe toe, keeps the tire in position when the tire pressure has decreasedand the tire receives a lateral force, thereby ensuring continued safedriving.

According to this example, the bead core is close to the rim flange andthe radial tire has the hump groove and the rim has the hump which fitsinto the hump groove. These arrangements enhance the power of the rim tohold the tire in place and hence ensure safer driving.

Incidentally, it is also possible to apply the above-mentioned beadstructure only to either of the beads.

CAPABILITY OF EXPLOITATION IN INDUSTRY

The present invention will be applied to various kinds of vehicles suchas passenger cars, motorcycles, tricycles, all-terrain vehicles, trucks,and busses.

We claim:
 1. An assembly comprising a wheel rim and a radial tire forfour-wheeled vehicles mounted thereon, said radial tire having an aspectratio of smaller than 60% comprising:a pair of beads; a pair of beadcores disposed one in each bead; a carcass extending between said beadsand turned up in both edge portions around said bead cores; a treaddisposed radially outside the carcass; a belt disposed between thecarcass and the tread; and a bead apex disposed between each of thecarcass turned up part and the carcass main part and extending radiallyoutward from the bead core,and said wheel rim comprising: a pair ofaxially spaced bead seats on which beads of the tire are seated; a welllocated between said bead seats to facilitate the mounting of the tire;and flanges extending radially outwardly from the axially outer edges ofthe bead seats, at least one of the beads provided with a radiallyinwardly extending toe in a portion axially inward of the bead core, anda circumferentially extending hump groove on the axially outside of saidtoe, said wheel rim provided, between the well and each of or one of thebead seats, with a circumferentially extending annular groove into whichsaid toe is extended, and a hump extended into said hump groove andlocated at the axially inner edge of the bead seat, the surface of saidtread being curved so that the axial width of the tread is wider thanthe maximum axial section width of the carcass, and that the axiallyouter edges of the surface are positioned at a height within a range of50 to 100% of the maximum cross-section height of the carcass, thethickness of said tread at both edges being within the range of 70 to200% of the average value of the thickness at the tread center and thethickness at the position three quarters of the maximum width of thecarcass measured from the tread center, said belt having at least oneply of organic fiber cords of which elastic modulus is lower than 1000kg/sq.mm having a width being within the range of 70 to 100% of theentire distance along said curved surface of the tread, each bead apexbeing made of rubber of which JIS(A) hardness is 74 to 95, and extendsup to 70 to 90% of the height of said axially outer edge of the tread,each of said bead seats having a width of a conventionally standardizeddimension so that the wheel rim can be accommodated to a conventionaltire having a bead devoid of a radially inwardly extending toe and acircumferentially extending groove.
 2. The radial tire wheel rimassembly as claimed in claim 1, wherein said tread is provided withsipes in extended parts in both edge portions.
 3. The radial tire wheelrim assembly as claimed in claim 1, wherein said belt has a belt ply ofhigh-modulus cords in addition to said belt ply of organic fiber cordshaving a low modulus and the width of said belt ply of high-moduluscords is smaller than 80% of said maximum width of the carcass.
 4. Theradial tire wheel rim assembly as claimed in claim 1, wherein said toeis made of 70 to 85 JIS(A) hardness rubber.
 5. The radial tire wheel rimassembly as claimed in claim 1, wherein the height from said bead seat,of a protuberant part lying between said well and said annular groove,when defining the axially inward extent of the annular groove, is notmore than 5 mm.
 6. The radial tire wheel rim assembly as claimed inclaim 1, wherein the depth of the said annular groove from the bead seatis not more than 10 mm.
 7. The radial tire wheel rim assembly as claimedin claim 1, wherein the height of said hump from said bead seat issmaller than 5 mm.
 8. The radial tire wheel rim assembly as claimed inclaim 1, wherein in said at least one of the beads, the bead core ispositioned such that the distance of the center thereof from the heelend of the bead is 1/2.5 to 1/7.6 of the distance between the heel endand the toe end.